The present invention relates to a transfer printing sheet for marking articles of synthetic fibers with a distinct colorfast design or pattern and having a soft hand or feel by heat transfer printing, and to the corresponding printing method and printed article produced thereby.
Designs or patterns are conventionally printed on shaped articles of synthetic fibers, by impressing the designed design on the article by the usual method of printing with a printing ink comprising a dye for synthetic fibers, and then subjecting the printed article to heating treatment with steam. Other known printing methods use pigmented resins which are prepared by admixing pigments with various synthetic resin emulsions, or printing inks in which synthetic resins are similarly contained as vehicles.
However, the former method wherein printing ink dyes are used requires a cumbersome process including a long period of heat treatment with steam, followed by washing with water for the removal of glue, drying, etc. for synthetic fibers of any given type; fails to produce a distinct design although the colored article retains a good hand or feel; and is totally unusable for colored fabrics since a white dye is not available which has hiding power as is necessary in such a case.
On the other hand, the latter method which uses pigments and synthetic resins in combination has the advantage that the design or pattern can be fixed by only a relatively short period of heat treatment or drying and in turn can be made colorfast when the synthetic resin is self-crosslinkable or is used conjointly with a crosslinking agent so as to be curable in the presence of a catalyst or moisture or by oxidation in air or irradiation with radiation; and has the further advantage that a white pigment can be used as desired.
Synthetic resins useful for the above mentioned method are chiefly polyacrylate copolymer resins, melamineformaldehyde resins, etc., which assure very satisfactory color fastness and exhibit resistant properties on cotton, hemp, rayon and like natural fibers, but which nevertheless are very low in strength on shaped articles of synthetic fibers which are chiefly polyester fibers and further include nylon, polyacrylyic and like fibers. Moreover, when crosslinked as described above, these resins seriously impair the hand or feel of synthetic fibers and do not always exhibit improved durability. Accordingly, these resins are normally used only for giving very pale color prints on synthetic fibers, and generally merely on blends with natural fibers.
To overcome the foregoing drawbacks of conventional methods, transfer printing methods have found wider use in recent years, although these methods still have drawbacks.
For example, the dry sublimation transfer printing method for polyester fibers is not usable for colored articles.
Also, the method employing heat transfer sheets which comprise a pigment and a meltable or thermoplastic synthetic resin in admixture makes use of the tackiness or thermal adhesion of the synthetic resin to give sharp patterns conveniently and economically. With this method, however, the resin coating is merely adhered to the article printed therewith by plastic flow contact with the otherwise unmodified fibers of the article, such that the print is low in durability, especially in resistance to rubbing and washing, like those prepared by direct printing.
Thus, extreme difficulties have heretofore been encountered in attempts at printing sharp colorfast designs or patterns on shaped articles of various synthetic fibers.